Update TeX.gitignore

Added a line that adds the `auto` folder that Emacs+ AUCTex automatically creates in the gitignore list. 

More about this `auto` feature below 
https://www.gnu.org/software/auctex/manual/auctex/Parsing-Files.html

Author: Vassilis

TeX.gitignore

@@ -192,3 +192,6 @@ TSWLatexianTemp*
 
 # KBibTeX
 *~[0-9]*
+
+# auto folder when using emacs and auctex 
+/auto/*